Electric heating pad



July 6,l 1943. F. LOBL ELECTRIC HEATING PAD Filed May 3, 1941 Invenozv.

Patented July e, 1943 UNITED STATES PATENT OFFICE 2,323,478 ELECTRIC HEATING PAD Frederick Lobl, Middleton, Mass.

Application May 3, 1941, Serial No. 391,728 9 claim. (ci. 21a-46) The present invention relates to flexible electrio heating pads wherein a heating conductor is disposed within the covers of the pad to dis-` tribute heat uniformly over both surfaces thereof.

Heating padsof the above typeare in common use and are effective therapeutic devices. These pads, in order to provide varying intensities of heat, are provided with a plurality of heating elements of different electrical resistance adapted to be electrically energized singly or in combination to provide the desired intensity of heat.

This method of supplying a plurality of heat intensities in the pad is relatively expensive since it involves the provision of a relatively expensive switch member and the provision of a plurality of thermostatic units for controlling the degree of heat of the pad. Because of this increase in cost, the number of heat intensities which would be provided in a single pad has been limited, usually tothree. To overcome this economic limitation and without materially increasing the cost of the pad, it has been proposed to provide a covering for the pad having surfaces of dissimilar heat conducting characteristics. Thus, one surface of the pad is provided with a sheet which is a relatively good conductor of heat and .fthe other surface of the pad is provided with a sheet which conducts heat at a substantially slower rate than the first sheet. Thus, with this arrangement, the effect of a high heat is obtained on one side of the pad and the effect of a lower heat is obtained on the other side without in any way affecting the connections to the heating element. 'I'his is a satisfactory method but involves some discomfort if not danger in use, since there is no means on the pad to indicate at all times which is the high and which is the lowheat side. Thus, a patient desiring to obtain the benefits of low heat unintentionally may have the high heat side placed in contact with a portion of his body which may be unduly sensitive to heat. Thus, he might be rendered uncomfortable, and even harmed, before the pad' was removed, or reversed in position, particularly, if

he were so disabled by illness that he was not able by himself either to move the pad or to break the electrical connection to the heating elements of the pad. i

An object of the present invention is to provide a construction wherein this discomfort or possible danger of injury to the patient or person using thev pad is effectively diminished.V

To this end, a featire of the invention resides in an electric heating pad having a heater element, and a cover member, either permanently connected with the heater element or separable therefrom, as a pouch from which the heater element can be withdrawn upon need, formed of materials providing the opposite faces of the pad with dissimilar heat conducting characteristics and the two surfaces having dissimilar appearances and feel. For instance, that side of the cover member providing the low heat side of the pad can be formed of a thick flannel-like material that is light in color and has a characteristic soft fluffy texture or feel. The other cover member, or the other side thereof, that provides the high heat side of the pad and has relatively high heat conducting characteristics, can have a color which differs distinctively in color from the color of the low heat side and which is formed of some material having a distinctive feel as, for instance, a characteristic stiffer or more rigid, as leather or rubber-like feel. Thus, with the pad embodying the presentinvention, the person using the pad, or the attendant, can on inspection determine readily by sight alone which is the high heat and which is the low heat side, or if the pad is under covers or the room is in darkness, the high or low heat side can be determined by the feel thereof. has the rubberized or leather-like construction and feel is the high heat side and the side which has the soft fluffy flannel-like feel is the low heat side. Thus, the differences in color and texture or f eel in the two surfaces of the pad are so marked that it would be impossible to mistake one side for the other. Hence, by the use of the pad embodying the present invention, discomfort and possible danger of injury to the user is prevented.`

A further object is to improve the construction and utility of electric heating pads.

With the above and other objects and features in view, the invention will now be described with reference to the accompanying drawing in which- Fig. 1 is a perspective view of a pad embodying the present invention with the plies at one corner of the pad separated more clearly to illustrate the construction thereof;

Fig. 2 is a plan view of the pad with certain of the cover members removed to illustrate more clearly the construction of the heating element;

Fig. 3 is a view in cross section taken along the line 3--3 of Fig. 1;

Fig.' 4 is an enlarged detail view illustrating the construction of the.heating element and its method of securement to a fabric liner member;

Fig. 5 is a view in cross section on a very much That is to say, the side which enlarged scale of that cover member having relatively high heat conducting characteristics; and

Fig. 6 is a view similar to Fig. `5, but illustrating that cover member having low heat conductlng characteristics.

The illustrated embodiment of the invention, as shown most clearly in Figs. 1 and 3, comprises a resistance heating element lll which conveniently is spirally arranged on a supporting fabric I2 although the specific arrangement is not herein of importance. The heating element Ill comprises a wire I4 ofsuitable electrical resistance which is wound in a spiral manner with spaced convolutions over a flexible core IB of suitable, as asbestos, fibres, and the composite element is provided with a covering iB formed preferably of asbestos fibres or of textile fibres which may be suitably treated to resist burning or charring. The heating element il.) thus constructed is stitched on to one face of the supporting fabric I2 by means of zig-zag or overcast stitching 2l, thus, firmly securing the heating element Il) to the supporting fabric l2. In the illustrated construction, the heater element ll) is arranged to provide two electrical circuits of different resist ance capable of being separately and also conjointly energized to provide three heats in a manner well known in the art and which need not be described in detail herein. Thermostats 22 are located in the electrical circuit of the heating element Il) for opening the electrical circuit when the temperature of any part of the heating element l0 exceeds a predetermined temperature. Said thermostats 22 are also well known in the art and need not be further described herein.

The supporting fabric sheet It' with the heating element Il) stitched thereto are interposed be tween suitable cushioning textile sheets 24 and 26. On the side of the sheet `I2 on which the heating element l0 is secured and on which the thermostats are located, the sheets 2B may be sev eral in number or a single thick Wadding for the purpose mainly of absorbing the thicknesses of the heating element and the thermostats, and on the opposite side of the supporting sheet l2, there is located a lesser number of sheets, and herein but a single cushioning sheet 24. The sheets 24 and 25 are formed of suitable, preferably open Weave, textile material of selected heat passing ability as a very highly napped cotton f material as flannel, or a sheet of Wadding.

The outer cover of the pad, which cover ls herein illustrated as permanently secured to the heater element, although it can be readily separable therefrom in a well known manner, is composed of two opposite cover members 3D and 34 formed of materials having different heat passing or conducting characteristics. One surface is covered by a cover member 3U which is formed of a soft fiuly textile material having relatively low heat conducting characteristics. As illus trated most clearly in Fig. 6,- the cover member 3U is a two-ply material having warp threads 3| formed of relatively tightly spun hard threads. 'I'he filling material preferably is formed by loosely spinning cotton bres about a relatively hard core thread 32. The two layers of Warp are connected together at spaced portions by having one of the filler threads 32 looped over a warp thread 2l in the other set. By the use of a lling thread Vformed as described above. the material after being woven may readily be napped to form a thick soft material having an infinite number of small air spaces so that heat is conducted relatively very slowly through the cover member 3l.

The illustrated cover member lll has a distinctively dlierent color or shade than the other cover member 34. For instance, the cover member 30 can be alight shade of tan, while the other cover member 34 can be maroon. These mentioned colors are merely illustrative, however, and other contrasting colors or shades can be used.

'Ihe cover member 34 is characterized by having a markedly higher heat conducting ability than that of the cover IB, so that in use it feels hotter than the cover 30. As illustrated, a cover member 34 very satisfactory for the purpose lncludes the cotton base fabric 38 which is provided on its outer face with a coating Il! preferably of rubber or other adhesive or impregnating material which is worked into the material 2B to seal the interstices between the threads. The coating 38 is applied in a semi-fluid or plastic and tacky condition to insure proper bonding o! the coating 3B to the fabric 36. While the coating 3B is in a tacky condition, flocking 4l) is preferably applied to the coating 38. This ilocking 4l) is preferably applied in an electrostatic held so that the fibres forming the flocking 4U on striking the coating 38 tend to stand endwise on and will im bed themselves slightly into the surface o! the coating 3B. The flocking 4D is formed of rela tively short textile fibres such as cotton, wool or any of the synthetic iibres such as rayon or celan ese, a synthetic fibre being preferred because oi its higher thermal conductivity. The libres arc so short that the hooked surface has 'the sllghtml 1y roughened appearance of a une quality of suede leather and has somewhat the feel oi suede leather.. lt is apparent that the cover member 5N because oi its appearance, feel and density, dii fers substantially from the feel and appearance of the other cover member 3D. The flocking can be omitted when not desired, however, in which case the coated or impregnated fabric surface will be directly exposed.

As shown most clearly in Fig. 3, the supporte ing fabric or sheet l2 having the heating ele ment lil stitched thereto, and the insulating sheets 24, 26, together with the cover members 30 and 34, are positioned one above the other in the proper order and are secured together at their longitudinal edges by stitching d2. lifter the members have been stitched along their longitudinal edges, the pad is turned right side out with the cover member 3l) on one side of the pad and the cover member 34 on the other side ol pad. The stitching about the open edge of the pad may then be completed in any suitable manlief.

The cover member 3l] is fiulfy and porous and on its outer surface is composed of iine libres that are good heat insulators. Hence, the heat lng effect of the kpad when this surface is in Contact with the body is produced mainly by direct radiation from the heating element llD through the outer cover member 3D.

The cover member 34, on the other hand, is impervious and is a relatively good heat conductor and the parts in contact With the body have large mass in contrast to the fine iibres Vof the cover member 30. The cover member 34 is heated by radiation from the heater element and of itself becomes hot and heats the body in contact therewith by conduction.

A thermometer applied to the outer face of the cover member 34 will indicate a considerably higher temperature, sometimes as much as twenty degrees, than when applied to the outer face of the cover member 30.

cover member 30 may be applied thereto depending upon the degree of heat intensity required for the affected body part. 'Because of the difference in feel and appearance, the patient or attendant does\ not need to Wait until the pad is heated substantially to its full temperature to determine which is the low and which is the high temperature side and can deter- .mine the desired side in the dark, by feel alone.

This, as before pointed out, is a safety factor not found in prior pads. Furthermore, this difference in texture and ifeel saves the time of an attendant, particularly in a hospital Where the attendant has a large number of patients to care for. In such a case, the high heat cover 34 or the low heat cover 30 may be placed next to the patient and in contact with the affected portion of his body, the circuit completed through the heating element l0, and the attendant may then promptly, without waiting for the pad to heat up,

go about her or his duties.

The high heat cover member 34 also is impervious to moisture as is desirable as it is the cover that when applied to the body is most liable to cause perspiration.

Having thus described my invention, what I claim as newand desire to secure by Letters Patent of the United States:

1. An electric heating pad. having opposed outermost exposed cover sheets both arranged for engagement withthe body of the user, an electric heating element disposed between and in heat influencing relation with said opposed sheets, said opposed sheets being composed of,

materials providing different heating properties and widely diilerent appearance and texture to denote by sight and touch their relative heat conducting properties, one of said sheets being of material and construction providing transmission of heat to the user largely by radiation from said heating element, and the other of said sheets being of material and construction largely precluding radiation therethrough and heating the body of the user mainly by conduction.

2. An electric heating pad having an electric heating element enclosed in a flexible casing having two opposed outermost exposed cover sheets constructed of materials having different heat conducting properties, one of said sheets comprising a relatively thin dense sheet of textile material coated exteriorly with a substance having heat conducting properties notably superior to the heat conducting properties of the textile material, and the other cover sheet being formed of a soft thick napped fabric having a relatively low heat conducting property, each of said sheets being arranged for selective engagef ment with the body of the user.

3. An electric heating pad having opposed covers, each arranged for alternate engagement with the body of the user and an interposed heating element, one cover having a flocked surface upon a relatively impervious backing and the other cover being pervious and presenting a surface of long loose bres.

4. An electric heating pad having opposed' covers, each arranged for alternate engagement with the body of the user and an interposed heating element, one cover being composed of a moisture-proof relatively high heat conductivity material and the other surface being composed of a relatively low heat conductivity material, the rst mentioned cover feeling hotter than the second cover. v

5. An electric heating pad comprising a heating element, and an enclosing cover having opposed cover members one characterized by being pervious and permitting heat of said heating element to be radiated through it and composed mainly of material of relatively low heat conductivity and the other characterized by being relatively impervious to radiated heat and by being composed of relatively good heat conducting material which is of itself heated by heat of said heating element and by imparting its heat by conduction to a body in contact therewith, eachof said cover member being arranged to alternatively engage the body of the user.

6. An electric heating pad as in claim 5, said one cover member being composed of a soft fluffy material of good heat insulation and said other cover member being a fabric having a heat radiation absorbing surface of relatively' good heat conducting material.

.'7. An electric heating pad having an internal heating element and an envelope said heating element having a high temperature body contacting surface that is relatively impervious to heat radiation and is composed of a relatively good heat conducting material and a low temperature body contacting surface that is pervious to heat radiation and is composed of relatively low heat conducting material.

8. An electric heating pad having an electric heating element and opposed body contacting sheets of materials of different heat conducting properties on opposite sides of said heating element, one `sheet being impervious and the other sheet being pervious to radiated heat.

9. An electric heating pad having an electric heating element and opposed body contacting sheets of. materials of different heat conducting properties on opposite sides of said heating element, one sheet having an impervious coating and the other sheet being pervious.

`FREDERICK LoBL. 

